Manual of Petroleum Measurement Standards Chapter …ballots.api.org/copm/colm/ballots/docs/COLM_6 _2A_1_18.pdfChapter 6—Liquid Flow Measurement Systems Section 2A— Truck and Rail

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Manual of Petroleum Measurement Standards Chapter 6—Liquid Flow Measurement Systems

Section 2A — Truck and Rail Loading and Unloading Measurement Systems

DRAFT FIRST EDITION

3_24_2016


FOREWORD

This standard covers the selection, installation and operation of loading and unloading metering systems.


Table of Contents

To be added in editorial.


Introduction

This standard serves as a guide in the selection, installation and operation of truck and rail, loading and unloading measurement systems. This section does not cover truck and rail mounted flow meters. This standard does not endorse or advocate the preferential use of any specific type of metering system or meter.

In general, metering system installations should meet certain fundamental requirements, including those that ensure proper meter type, size, installation and adequate protective and readout devices (such as presets, registers [counters], strainers, relief valves, pressure and flow control valves, and air eliminators, where required). Descriptions of these and other system components are covered elsewhere in this standard or other API standards. Also, to ensure compliance with state laws and regulations the latest editions of NIST Handbook 44, Handbook 12, as well as specific local weights and measures requirements, should be considered.


Chapter 6—Liquid Flow Measurement Systems Section 2A— Truck and Rail Loading and Unloading Measurement Systems

1 Scope This standard (section 6.2A) is part of a set of documents which detail the minimum requirements for the design, selection, and operation of truck and rail loading and unloading metering systems for single phase liquid hydrocarbons.

1.1 Field of Application Sections of Chapter 6 describe metering system design. Section 6.1A describes the general considerations applicable to all metering systems and shall be consulted together with this section, Section 6.2A, when designing systems. For the purpose of Chapter 6.2A, the equipment which is covered as part of a truck or rail, loading or unloading meter system will be limited to that which is necessary for the proper operation, calibration and performance of the primary, secondary and tertiary devices as well as equipment that can affect the agreement between the ticketed (also called quantity transaction record, batch ticket, or measurement ticket) and delivered quantity. When aspects are covered under the scope of other chapters of the API Manual of Petroleum Measurement Standards, and to avoid replication and conflict, they are not covered by this standard. In these cases, this standard provides limited information and refers the user to those chapters.

2 Normative References The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

API Manual of Petroleum Measurement Standards (MPMS), Chapter 4.6, “Pulse Interpolation” API Manual of Petroleum Measurement Standards (MPMS), Chapter 5.2, “Measurement of Liquid Hydrocarbons by Displacement Meter” API Manual of Petroleum Measurement Standards (MPMS), Chapter 5.6, “Measurement of Liquid Hydrocarbons by Coriolis Meters” API Manual of Petroleum Measurement Standards (MPMS), Chapter 6.6, “Pipeline Metering Systems” API Manual of Petroleum Measurement Standards (MPMS), Chapter 11.1, “Physical Properties Data” API RP 2003, Protection against Ignitions Arising Out of Static, Lightning, and Stray Currents NIST Handbook 44, Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices

3 Terms and Definitions For the purposes of this document, the following terms and definitions apply. Terms of more general use may be found in the API MPMS Chapter 1 Online Terms and Definitions Database.

3.1 transloading the transfer of a commodity from one mode of transportation to another mode of transportation. An example of transloading is when a commodity is transferred from a truck into a railcar. 3.2 preset controller(s) A set of electronic equipment and/or software that is adjusted/configured beforehand to facilitate installation and use. Measurement presets implements algorithms using analog and digital signals received from meters, temperature transmitters, pressure transmitters, and density transmitters to calculate volumes at base conditions. These are sometimes referred to as preset, electronic preset, preset counter, batch controller, or preset instrument.


3.3 Terminal Automation Systems (T.A.S.) comprehensive programs with human machine interface (HMI) that manages a facility’s commodities’ movements, inventory control, and reconciliation through automation.

4 Loading, Unloading, and Transloading Metering Systems

4.1 General The loading, unloading, and transloading metering systems described in this standard are those that apply to transport-type truck and rail facilities. These measurement systems (including for example all devices addressed in Chapter 6.2A) should be designed to accommodate the full range of process conditions to be encountered. The design of the system should allow one meter to be proved without interfering with the other meters involved in the loading operations.

Different than truck loading and unloading metering systems which can only handle a single truck; multiple rail cars can be loaded simultaneously. Simultaneous loading or unloading of multiple rail cars through a single meterbank will result in a single quantity determination which represents the quantity transferred for all of the cars. Having a single ticket representing multiple rail cars can cause issue when reporting requirements, perhaps from government or regulation, dictate individual bills of lading. The configuration and count of rail car metering systems may require an evaluation of the ticket requirements. Options for rail unloading and loading metering systems may require a combination of the following data sources:

1. Quantity determination

a. Meter run dedicated to each rail car (quantity determined per car)

b. Meter run(s) dedicated to a string of rail cars (quantity determined per string of cars)

2. Quality determination (e.g. Density or S&W)

a. Sampler dedicated to each car (determination per car)

b. Sampler dedicated to a series of rail cars

c. Sampler dedicated to a predetermined batch volume for a rail movement

Note other local or national regulations or guidelines could apply (for example, in the USA, Handbook 44).

4.2 Loading, Unloading, and Transloading Metering System Installation Loading, unloading, and transloading metering systems are intended to determine accurate quantities of products into or off of transport truck and rail cars. The metering configurations may consist of single product meters, blend meters and additive meters. Design, installation, and operation of the meter system is extremely important because meter volumes are considered in custody transfer and loss/gain determination. Note that the loading and unloading system is usually the final opportunity to measure accurately, i.e., after the product leaves the loading and/or unloading facility, measurement errors are difficult to correct.

Considerations for proving equipment should be taken into account during design and installation. See 8.1 of this document for additional information about proving.

4.2 Loading operation

4.2.1 Top Loading Because State and Federal regulations govern the release of hydrocarbon emissions to the atmosphere, some forms of top loading may not be acceptable. Personnel safety should be considered in top loading system design.


Top loading (see Figure 1) uses an overhead-loading arm to reach the loading dome hatches on the truck and railcars. The loading arm should be in the same state of fill—either void or full—at the beginning and end of the loading operation to ensure measurement consistency.

Figure 1—Installation Diagram Metered Truck and Railcar Loading (Top Loading)

Top loading arms that have been designed to be completely empty when not in use should be equipped with a manual or automatic vacuum breaker located at the high point in the piping and downstream of the loading valve. This provision allows the arm and drop tube to drain after the loading valve is closed preventing product from being retained in the arm and unintentionally being delivered with the next batch.

Meters for top loading systems can be located on the loading platform or near the ground. When the meter is located below the platform, consider locating the meter register and/or preset to facilitate the reading of quantities by the loader. A preset device, either local or remote, may be installed in any loading system to expedite loading operations.

4.2.2 Bottom Loading There are no measurement concerns related to bottom loading. See figure 2 for a typical installation.


Figure 2 —Installation Diagram—Metered Truck and Railcar Loading (Bottom Loading)

4.3 Unloading While unloading systems use many of the same components associated with loading there are some special considerations that need to be addressed for proper measurement. The typical components of an offloading system are a meter, a pump, an air eliminator, strainers, check valves, and proving connections.

4.4 Transloading While transloading systems use many of the same components associated with loading there are some special considerations that need to be addressed for proper measurement. The typical components of a transloading system are a meter, a pump, an air eliminator, strainers, check valves, and proving connections. This system may be a permanent installation or portable. When a portable system is used there are additional things to consider. When installing transloading systems it is important to mitigate any system interference, the metering device’s operating principles should be considered and appropriate precaution should be observed.


4.5 Loading And unloading Accessories

4.5.1 Strainers and Filters Suspended solids in the fluid being measured can cause inaccuracy and even damage metering equipment. Solid particulates should be prevented from reaching the meter by using an appropriate strainer or filter per meter manufacturer’s recommendations. Filters are typically utilized in jet fuel, bio-fuels and distillate applications in lieu of strainers. The strainer or filter should be monitored and/or checked periodically to avoid restricting flow which could lead to vaporization, or reduce the normal flow rate and thereby affect accuracy by causing the system to deviate from the flow conditions when the metering system was proved.

4.5.2 Air Eliminators Air eliminators are required in systems where air or vapor can be introduced into the system. If not eliminated, air will adversely affect measurement and may cause damage.

Additional information is available in Annex A of this chapter.

If air eliminators are installed, they should be installed upstream of the meter, and their purpose is to dispose of any air or vapor in the delivery line before it passes through the meter. If a system is designed so that significant amounts of air, vapor, or both cannot be introduced, an air eliminator is not required.

A sight glass can be located between the air eliminator and the flow meter to check the functionality of the air eliminator and to ensure the piping between the unloading arm coupler and meter is always full of product.

4.5.3 Insulation or heat tracing Unique properties of the petroleum or petroleum product(s) being measured may require the individual components or the entire system to be insulated and/or heated. The purpose of the insulation or heat trace is to preserve the process conditions. For example, high viscosity crude oil which is heated to increase Reynolds number. Another example could be a low temperature commodity such as light liquid hydrocarbon (LLH), cooled below vapor pressure. Measurement of such commodities outside their desired state may impact measurement performance.

4.5.4 Thermal Relief Systems Due to the need for thermal relief systems to have an open flow path to a lower pressure location and that thermal relief valves do not provide positive isolation, thermal relief valves can directly affect measurement accuracy if they are located between the meter and the prover, or between the meter and the transport.

4.5.5 Vents Liquid metering systems shall be designed with the necessary facilities to handle vapors and non-condensable gases (“gases”) when they are (1) trapped within the piping, (2) introduced from the incoming flowing stream or (3) formed due to flashing of the liquid. When not addressed gases within a liquid metering system may cause equipment damage as well as inaccurate measurement and calibration.

Metering system designs should provide a means to remove gases and vapor, e.g. a vent, from any areas where they could become trapped. With vent taps comes the potential for leakage or spill-over. If vents are located upstream of the meter and prover or downstream of the meter and prover then leaks and spill-over could cause a difference between the balance of the quantity transferred and the quantity ticketed. If vents are located between the meter and prover, any leaks or spill-over could affect the measurement accuracy. If a vent or tap that cannot be avoided by improving the piping configuration, a means of positive shut off shall be provided at each vent tap point.


If gases are intermittently introduced into the incoming, flowing stream a high point vent will not provide a solution unless it is combined with an air eliminator to trap the gas and a valve to release it based on liquid level. (Refer to MPMS Chapter 6.1)

High point vents should not be used as a solution to gases formed from continuous flashing or cavitation. Gases formed by continuous flashing or cavitation should be solved by maintaining adequate back pressure. (refer to paragraph 6.1 Back Pressure Control.)

4.5.6 Drains Metering system designs should include taps at low point locations such that liquids may be drained before maintenance. With drain taps comes the potential for leakage when they are not in use. When drain taps are located upstream of the meter and prover or downstream of the meter and prover then leaks could cause a mismatch between the quantity transferred and the quantity ticketed. When drains are located between the meter and prover and there are leaks or spill-over then the measurement accuracy will be affected due to erroneous calibrations. Any drain that can affect measurement accuracy or cause a difference between the quantities transferred and the ticketed quantity shall be equipped with a means to verify that no leaks exist.

4.5.7 Pumps System hydraulics can affect meter performance. System pumps and controls should be designed to meet the desired operation of the facility such that adequate pressure and flow are provided.. The ability to prime the pump and the effect of fluid properties, such as density and viscosity, should be considered when selecting pumps. The location of the pump relative to the meter should be considered if vibration or pulsation will affect the meter performance.

If pumps are capable of pressure exceeding any equipment rating in the measurement system, over-pressure protections should be put in place.

4.6 Valves

4.6.1 Isolation/Secondary Shutoff Valves Inlet/isolation valves are related to isolation, bypass and evacuation of piping associated with the measuring system. Each, given its respective position in the piping configuration and its operation, can have unintended consequences adversely affecting measurement if they present an opportunity for liquids to bypass the measuring elements (meters and associated instrumentation, including sampling systems).

4.6.2 Check Valves Check valves are required to prevent backflow, siphoning with low tank head (low pressure), and cross contamination of product during blending applications. When choosing the proper check valve, consider pressure drop and slamming of the flapper, which can cause damage when the valve opens and closes.

For unloading it is recommended to install a check valve on the discharge line. This will keep product from coming back from the tank when the pump is shut off. If the air elimination line is tied into the delivery line downstream of the meter it should have a check valve and some way of verifying the operation of the air eliminators product shut off functionality. These are necessary to prevent unmeasured product from flowing either direction and bypassing the meter.

4.6.3 Control Valves Control valves are used to control process variables such as flow or pressure by fully or partially opening or closing to achieve the desired conditions. A "set point" for process control to a process variable value may be provided manually, or by an automated process controller.


If control valves are used to maintain back pressure, they should be installed downstream of the meter. The control valve location should not negatively affect meter performance.

Severe shock to loading systems can occur unless certain precautions are taken in the design of the delivery facilities, in the construction of the facilities, or in both. Closing the loading or control valve too rapidly may cause hydraulic shock which can damage or change the performance of the meter. This condition may be avoided by controlling the rate of closure of the valve involved. The use of slow-closing valves or the control of the rate of closure on the loading arms is recommended to reduce line shock. The occurrence and severity of line shock depend on flow rate, shutdown rate, and length and size of lines. When preset devices are used, a two-stage start-up-and-shutdown valve should be incorporated to start the flow slowly before it allows full flow to develop and to slow the flow down shortly before the final shutoff. Additional information related this topic can be found in Annex XThe manufacturers’ recommended flow control range should not be exceeded. This could result in poor flow control, unsafe shutoff, inaccurate measurement, and premature wear.

5 Meters

5.1 General This section covers the characteristics of loading and unloading meters and discusses only those considerations unique to the design, selection, installation, and performance for chemicals, liquid hydrocarbons, and bio-fuels.

Historically, truck and railcar loading and unloading systems were designed for use with displacement meters; however, technological advances and blending applications have encouraged the introduction of other meter designs such as turbine and Coriolis meters. When retrofitting existing displacement metering systems with turbine and Coriolis meters, care should be taken to ensure proper application of these technologies. API MPMS Chapter 5 defines the installation of meters. Make certain that any areas that may trap or build up with debris are avoided. Avoid installing the meter at a high point in the piping to prevent trapping air in pockets and causing mismeasurement.

Metering systems can be used to determine the total quantity (volume, weight, or both) being loaded. Metering systems generally include a flow meter (either volumetric or mass), appropriate temperature and pressure instruments for compensation to standard reference conditions, and a flow computer to collect the instrument signals, perform the necessary calculations, and produce a final run ticket or quantity report. The meters and accessory equipment require periodic proving, calibration, or verification to ensure they are in good working order. See API MPMS Chapter 6.1A for additional information about accessory equipment. The frequency and tolerances are set by the manufacturer, equipment owner or contract terms. Specific guidance for tolerances is also provided within the applicable API standard. Refer to API MPMS Ch. 5 and API MPMS Ch. 7.

5.2 Displacement Meters Displacement meters (API MPMS Ch. 5.2) will require some form of signal output, either electronic (preferred method) or mechanical. Meter readout adjustment methods are discussed in MPMS Chapter 5.2, Section 5.2.5.1.

Please note that when a meter originally furnished with a manual calibrator is retrofitted with an electronic pulse transmitter, the transmitter shall be mounted below the calibrator or the calibrator needs to be removed.

Displacement meters typically can be mounted either vertically or horizontally. Consult the manufacturer for proper orientation to prevent issues related to bearing load and wear. Displacement meters do not require flow conditioning. See Figure 3 for a typical installation.

Displacement meters should be considered for loading and unloading applications which present a wide variation in flow rate. This may be more critical when a single meter factor is used to represent the batch.


Figure 3—Typical Displacement Meter Loading Configuration

5.3 Turbine Meters The performance of turbine meters (API MPMS Ch. 5.3) is affected by erratic or inconsistent flow profile caused by upstream or downstream devices and obstructions, such as strainers, valves, pipe internal diameter irregularities.

Fouling or plugging or a flow conditioner or meter will cause flow distortions and affect meter performance. Maintenance performed on the meter or flow conditioner to remove fouling or plugging requires that the meter be re-proved.

The influence on pressure drop/flow rate varies depending on the type of flow conditioning applied; this needs to be considered in the overall system design.

For loading, unloading, and transloading systems turbine meters may be mounted either horizontally or vertically. Meter performance could be affected by installation orientation. Follow manufacturer’s recommendation. See figure 4 for a typical installation.


Figure 4 —Typical Turbine Meter Loading Configuration

5.4 Coriolis Meters For Coriolis meters (API MPMS Ch. 5.6) mounting orientation can cause unwanted effects. Any air in the sensing tubes will create errors in the measurement system. Consult with the manufacturer for specific installation requirements. Coriolis meters do not require flow conditioning (see Figure 5).

A means should be provided to isolate the liquid full meter under no-flow conditions for zeroing purposes, in accordance with the API MPMS Ch. 5.6. Selection of a Coriolis meter in a loading or unloading application requires consideration of the proving method and/or the locally available portable provers. Consult both the meter manufacturer and the prover operator for assurances that the paring will work.


Figure 5 —Typical Coriolis Meter Loading Configuration

5.5 Electrical Installation Truck and railcar loading, unloading, and transloading systems may include a variety of electrical and electronic accessories. The electrical system should be designed and installed to meet the manufacturers' recommendations, as well as any local, state, city, national, or company regulations as applicable. Noise inducement and signal interference with the meter pulse signal, which can adversely impact measurement, shall be avoided. The classification of the area should be known and understood in order to comply to any regulatory requirements.

5.6 Flow Rates Meters should be sized to accurately measure flow at minimum and maximum flow rates. All operational flow rates should be known so the metering device can be proved and calibrated correctly (Refer to section 8 of this document).

For additional information on flow rates and their effects on operations refer to API RP 2610 and API RP 2003.


5.7 Pressure Drops The addition of a prover to the flow path will change the flow resistance. Depending on the pump selection and arrangement of parallel loading/unloading connections, the increased flow resistance may lower the flow rate on the meter being proved away from its normal operating rate and may affect the meter factor.

5.8 Orientation and location of meter Meter performance can be affected by installation orientation. Follow the manufacturer’s recommendations for orientation. Flow meters shou ld be located as near as practicable to the rail car or tank truck being loaded or un loaded to mitigate the possibility of a partially full line. If the line is not completely full, the metered quantity might not match the loaded quantity. If the meter cannot be located in close proximity, the loading facility should have a procedure to ensure consistent line fill. Following a consistent procedure will ensure that errors between the metered quantity and the delivered quantity are not introduced.

5.9 Meter and control valve sizing All meters and control valves have minimum and maximum ranges with respect to both flow rate and pressure and should only be operated within these ranges. When designing or retrofitting a multiple arm loading system the system should be checked at the extremes of operation to assure that all meters stay within operational parameters no matter how many arms are operating. Consult the manufacturer’s specifications for meter and valve sizing and recommendations.

Final product recipe components can vary greatly in both the volume and rate that they are loaded. It is necessary to be certain that any recipe and the associated percentages of the components of the recipe fall within the linear and repeatable flow ranges of the meter and control valve.

5.10 Meter selection Meter sizing should be determined by, but not limited to manufacturer recommendations, turndown, linearity, viscosity range, flow conditions, pressure drop, and product composition. For additional information, refer to Chapter 5.

Many loading and unloading systems are designed for typical maximum rates of between 500 and 700 GPM. For either bottom or top loading, it is desirable to start the load with a low flow condition to ensure adequate compartment head to minimize splashing, vaporization, and static electricity. If this is the case, the meter shall be sized to account for this low flow condition.

6 Auxiliary Meter Equipment

6.1 Back Pressure Control Conditions that contribute to flashing and/or cavitation of the liquid stream as it passes through the meter can be avoided through suitable system design and operation of the meter. Sufficient pressure within the meter can typically be accomplished by using control valves or back pressure valves. In the absence of a manufacturer's recommendation, the numerical value of the minimum pressure at the outlet of the meter may be calculated with the following expression, which has been commonly used. The calculated pressure has proven to be adequate in most applications, and it may be conservative for some situations.

Pb » 2DP + 1.25*Pe (1)

where

Pb = minimum back pressure, pounds per square in. gauge (psig),


DP = pressure drop through the meter at the maximum operating flow rate for the liquid being measured, pounds per square in. (psi),

Pe = equilibrium vapor pressure of the liquid at the operating temperature, pounds per square in. absolute (psia), (gauge pressure plus atmospheric pressure).

For additional information of back pressure control valves and/or control valves refer to section 4.6.3 of this document.

6.2Temperature For type of temperature sensors, and, transmitters along with the temperature calibration, correction, and calculations refer to Chapter 7.

6.2.1 Location of Temperature Sensor The placement of the temperature sensor is critical to accurate temperature measurement. API MPMS Chapter 7 defines the sensor location and number of sensors required. The most common methods of performing automated temperature correction are outlined in the Preset Section 13 and Terminal Automation System Section 15. In both cases, it is important that the temperature measuring device is properly calibrated according to MPMS Ch. 7.

6.2.3 Automatic Temperature Compensation Devices

Mechanical Live Measurement of the temperature can be used but may result in increased uncertainty.

6.3 Pressure Pressure compensation is required whenever the loading and unloading meter is above atmospheric pressure. The pressure during proving operations and normal operations shall be accounted for. Refer to MPMS Chapter 6.1A and MPMS Chapter 12.2.

Since pressure affects the calculation results, a fixed CPL/CMF should not be allowed to be used if the delta pressure is outside of a user’s tolerance. For LPG loading and unloading operations, pressure measurement is necessary for both meter proving and ticket volume determination.

6.3.1 Location of Pressure Measuring Device If correction for elevated meter pressure is required, the pressure measuring device shall be installed such that it does not interfere with the performance of the meter, but is representative of the pressure within the meter. The pressure measuring device can be either a pressure gauge or an electronic transmitter.

6.3.2 Calibration The pressure measuring device shall be verified on a periodic basis against a device that is traceable to a national standard.

7 Additive Measurement Additives shall be accounted for on the final ticket. This can be accomplished either by injecting the additive upstream of the custody transfer meter or by measuring the additive separately before injection. In multi-compartment cars, it may be necessary to account for the additive injected into each compartment.


Injection of additives upstream of the main custody transfer meter is the typical configuration used for additive injection. It may require a higher injection pressure than downstream of the meter due to pressure loss through the meter. Depending on the meter technology applied, careful selection of the injection point may be required such that the location does not interfere with the product flow pattern.

8 Meter Proving

8.1 Methods The method used for proving loading and unloading meters will determine loading and unloading design requirements. In choosing a proving method factors such as time constraints, truck and rail lane dimensions, number of meters, and availability of product return lines should be considered. Refer to API MPMS Chapter 4 for proving requirements and to API MPMS Chapter 6.1A for additional references. The proving frequency may be based on throughput volume, time, weights and measures requirements, seasonal temperature changes, historical meter performance, a combination of these factors, or contractual requirements. In addition, meters should be re-proved when subjected to repairs or changes that may affect measurement accuracy. When using electronic presets with multiple flow rate configurations, the establishment of multiple meter factors may be required (see section 9). This is particularly true when low flow start-up and shutdown sequences are employed to prevent system shock and static electricity generation (see API RP 2003).

The meter should be proved as close as practical to the same conditions under which it normally operates. Care should be taken to ensure that the pressure drop created by the prover’s piping, valves, and hoses, does not reduce the flow rate to an unacceptable level during proving. Caution should be exercised to ensure normal operating flow rates can be achieved through the entire proving system. Loading and unloading systems typically incorporate low flow startup and shutdown sequences to reduce static electricity (see API RP 2003) and system shock. These changes in flow rates can affect meter accuracy and are included in each calibration run. Due to the size difference of the prover and truck and rail compartments, the accuracy of the calculated meter factor may be adversely affected for meters with poor linearity. When meter linearity is not sufficient, it is recommended that meter factors be utilized to correct for inaccuracies for each operational flow rate (i.e., low and high flow rates). To help correct for the above inaccuracies the low flow rate factor should be established and applied prior to proving at the high rate.

8.1.1 Volumetric Provers (Tanks or Cans) The tank or can method provides a direct volumetric comparison between the meter under test and a national metrology-certified volumetric prover. Variables such as size, construction material, and design should be considered when selecting a volumetric prover. API MPMS 4.4 defines the criteria for volumetric provers. It is also important to ensure that normal operating conditions are reproduced during the proving process. Vapor recovery hoses and grounding equipment should be connected prior to beginning the process and flow rate stability should be achieved.

8.1.2 Displacement Provers Displacement provers can provide a convenient, accurate, and expeditious method for calibrating loading and unloading meters.

8.1.2.1 Displacement provers with 10,000 whole pulses or greater API MPMS Chapter 4.2 defines the pulse count requirements that are necessary for the prover to provide accurate proving calculations in accordance with API MPMS Chapter 12.

8.1.2.2 Displacement provers with less than 10,000 whole pulses (small volume prover) Displacement provers generating less than 10,000 whole pulses can be utilized for proving meters. API MPMS Chapter 4.6 defines the pulse interpolation techniques to be employed. These devices can be very compact and are conducive to proving directly into an awaiting delivery truck and rail. Meter factor determination is accomplished using the same requirements described in the above section.


8.1.3 Master Meters The master meter method involves the use of a master meter that has been calibrated prior to its use and will serve as a standard to determine the accuracy of another meter. API MPMS Chapter 4 defines use of master meters for proving.

8.2 Proving Conditions Loading and unloading meters should always be proved under the same conditions experienced during normal operation. These conditions include product composition (density and viscosity), flow rate, pressure, and operating temperature. Significant product temperature changes can affect meter accuracy and can necessitate additional meter proving to compensate for liquid density changes and dimensional changes to measurement equipment material.

Inappropriately sized supply pumps or piping systems may cause a reduction in flow rate when multiple risers of the same product are in service. Special procedures may have to be developed to ensure that normal operating conditions are achieved during the proving process. In addition, normal operating parameters can require adjustment in order to ensure consistent flow rates during heavy demand periods. These procedures may include using multiple meter factors and step flow rate control to ensure meter accuracy during periods of varying flow rates. Another option is to limit the maximum loading flow rate at each loading arm to ensure stable flow rates during multiple lane demands.

API MPMS Chapter 12 defines the corrections to be made for any changes in volume resulting from the differences in liquid temperatures between time of passage through the meter and time of volumetric determination in the prover.

Refer to API MPMS Ch. 4.8 for additional information about operating a proving system including operating above vapor pressure when using displacement or master meter proving.

8. 2. 1 Proving When Transport is at Atmospheric Pressure When the normal custody transfers are made into a truck and rail car at 0 psig, and the loading and unloading design does not use pressure transmitters to correct the meter pressure to 0 psig, a composite meter factor will have to be applied to ensure system accuracy.

This can be accomplished in either of two ways.

1. In the first method, both the meter and prover volumes are corrected to standard pressures (0 psig) while proving. The resulting meter factor is then multiplied by the liquid compressibility factor (CPL) of the meter (using nominal operating pressure), creating a composite meter factor to replicate the normal custody transfer.

2. In the second method, the meter pressure is disregarded while proving, with the resulting meter factor incorporating the CPL at the meter; however, if the prover is at a pressure other than zero then the prover volume is corrected to standard pressure to replicate the normal custody transfer.

For both methods, meter pressure fluctuations should be negligible, so that the meter pressure effect will be consistent when making normal custody transfers and when proving.

8.2.2 Proving When Transport is above Atmospheric Pressure If the normal custody transfer is made into a truck or rail car and the meter pressure(s) are corrected to base conditions, both the meter and the prover volume are corrected to base conditions when proving (standard conditions). These conditions could require pressure measurement at both locations.

8.2.3 Proving of Blending Systems Blending systems generally incorporate an electronic preset or flow computer to control the process. The preset or flow computer measures the volume of each component and assures the proper mixture by automatically controlling


individual control valves. Today’s electronic presets typically have the capability of applying multiple meter factors to correct for changes in flow rates and product type. Care should be taken to ensure that each loading scenario is understood and duplicated during meter proving.

8.2.4 Sequential Blending In order to ensure accuracy during this process, the single meter used for sequential blending will have to be proved for each product and at each flow rate. To help ensure homogeneous mixtures, systems may be configured to alternate the components in a sequence that divides the required volume of a single component into two stages to assist with mixing (e.g., for midgrade gasoline, the regular component volume can be divided into two separate stages: one before and one after the premium gasoline).

During the blending operation each component product will typically cycle through low flow startup and shutdown and continuous high rates. These set points should be accounted for during meter proving.

8.2.5 Ratio Blending Because multiple products are simultaneously flowing during ratio blending, product measurement can be adversely affected by the piping configuration and flow control. Flow rates will at times vary during the loading process due to back pressure caused by competing streams. The electronic presets are configured to achieve a final mixture ratio and often will significantly reduce the flow rate for one stream to allow the other(s) to deliver the required quantity. When this occurs, individual meters can be subjected to substantially reduced flow rates, causing inaccurate measurement.

Minimum and maximum flow rates should be determined to facilitate meter proving. The proving process should include all possible flow scenarios to help ensure accurate measurement. A method to address this issue is to use meter factor linearization.

8.2.6 Fall Back Flow Rate If operational conditions prevent the preset high flow rate from being achieved or maintained, a predetermined fallback flow rate may be applied. A fallback rate is applied to reduce the flow to a controllable level. This will ensure that the speed of operation of the loading valve is sufficient to prevent overfill. The number of flow rates can be adjusted to meet the particular installation requirements but normally would be set at decreasing flow rates between the programmed high and low rates. Once conditions permit, the electronic preset can automatically return to the desired flow rate. For configurations where a fallback flow rate is used, the meter should be calibrated at this fallback flow rate.

9 Meter Factor When a reduction in flow rate occurs due to operational conditions such as intermittent excessive pumping capacity demand, measurement accuracy can be adversely affected. For typical operations where flow rates may vary, it is advisable to prove the meter at multiple flow rates. At least two flow rates should be used: a slow flow rate for initial flow and a high flow rate at which the majority of product will be loaded. A meter factor linearization function in the electronic flow computer should be available to be configured to allow the preset to be able to select the meter factor closest to the flow rate being used or provide a meter factor linearization between two adjacent factors.

9.1 Sealing Metering Equipment All meter system accessories affecting the accuracy of volume measurement should be sealed, and all outlets or connections through which unmeasured withdrawal is possible should be sealed. Weights and measures regulatory agencies and NIST allow either electronic audit trails or sealable switches where electronic systems are installed.

9.2 Security API MPMS Chapter 21.2 defines the safeguards to be included to prevent improper changes to input variables which may affect measurement. A protect switch that safe guards relevant parameters, mechanical construction and/or an electronic audit trail should be utilized for this purpose. If a switch or mechanical means is utilized, then provisions should be provided that allow placement of seals or locks through the switch and the enclosure. The


program protection switch should make all parameters that affect measurement read only and inaccessible unless the seal is broken and this switch is activated. The electronics enclosure should not be accessible without first breaking the seal to visibly indicate violation of sealed status. If the audit trail method is utilized then the preset controller should be programmable to prompt for a unique password to select the programming of parameters. (For examples on audit trail implementation see API MPMS Chapter 21.2.)

10 Grounding Systems API RP 2003 defines the requirements for system grounding and bonding that can also generate a system shutdown. This may cause multiple tickets to be created for a single transaction.

This precaution against ignition will minimize the accumulation of static electricity on the tank truck and rail shell but cannot ensure the dissipation of all static electricity within the system. Grounding the tank truck and rail does not prevent the accumulation of static electricity in a liquid with poor conductive properties.

11 Overfill Protection Systems API RP 1004 defines the requirements for automatic tank overfill protection that can also generate a system shutdown. This may cause multiple tickets to be created for a single transaction.

12 Calculations of Quality and Quantity Refer to MPMS Chapter 6.1 for volume and/or mass calculations.

Weights and measures authorities typically require that the weighted average product temperature be printed on invoices for customers that are billed at net standard volume. For this reason, a temperature correction system should be used. In addition, automatic temperature correction can greatly aid facilities in the reconciliation of product inventories.

See API MPMS Chapter 12 for information on calculations.

13 Preset

13.1 General Presets are electronic and/or mechanical devices used in conjunction with metering devices and instrumentation to calculate incoming data into volumes or mass at base conditions. Presets may also be called lane controllers, batch controllers, or unit control devices.

13.2 Electronic presets Most electronic preset instruments are capable of correcting to gross standard volume (GSV) that includes indicated volume, meter factor, temperature and pressure compensation. When using the preset to calculate for temperature correction incorporating CTL (correction for the temperature of a liquid), the temperature measuring element is connected directly to the preset, and the preset calculates the volume based on a measured temperature. When using the preset to calculate for pressure compensation incorporating CPL (correction for the pressure of a liquid), the pressure measuring element is connected directly to the preset, and the preset calculates the volume based on a measured pressure. When utilizing these types of volume correction, it is imperative that the preset applies the proper volume correction factor for the given product based on the appropriate tables from API MPMS Ch. 11.1. It is also imperative that the proper product gravity is applied when calculating the volume correction factor.

13.3 Mechanical presets a) A mechanical preset is a non-repeating, predetermining counter that is driven by and normally mounted

on a flow meter; generally for use on positive displacement (PD) meters. A two stage output interface on


the preset is used to control a valve in two stages (low flow and high flow rates). The mechanical registration is adjusted by calibration in the flow meter.

b) Mechanical presets are available with various accessories that usually include a mechanical ticket printer that is mounted directly on the preset that will indicate the amount of liquid volume that was delivered for a preset operation.

c) Some systems use automatic temperature compensation devices (e.g., ATC/ATG). The ATC is a mechanical meter mounted temperature compensator that requires a fixed gravity selection. The ATG is a mechanical meter mounted temperature compensator that offers the operator an adjustable gravity selector system. Meters equipped with either the ATC or ATG provide for a temperature corrected volume registration on the mechanical preset.

14 Operations Load and unloading operations can be controlled using an electronic preset. This device is a batch controller specifically designed for automated loading and unloading operations. It can operate in either a standalone or automated mode when interfaced with a Terminal Automation System (TAS). It provides the required measurement data during loading for the bill of lading (BOL) printout by the TAS, or by a printer in standalone mode. The electronic preset can support the various blending operations as described in Section 13 or straight product loading and includes a staged flow profile used for product transfer. Additional typical preset functions include:

a) Individual product measurement profiles to apply the unique measurement characteristics to each product it is controlling. Configurable parameters such as meter factor, volume correction factors, temperature and pressure compensation factors with selectable units of measurement including volumetric measurement and mass measurement. Configurable individual product flow profiles to maintain accurate flow control rate parameters within the specified meter(s) range of operation for accurate measurement at all times. Some of these include: minimum and maximum flow rates, flow tolerance, first and final trip volumes.

b) Configurable discrete inputs and outputs to associated flow control and measurement devices, permissives for safety such as vehicle grounding and compartment overfill protection and various other load rack device interfaces should be included.

c) Support for multiple additive injection control and monitoring for products where additives or dyes could also be required.

d) Communications ports, Serial and/or Ethernet ports, that support Terminal Automation Systems (TAS), Additive Injection Systems, Card Readers and other various communicable interface devices may be included

e) Printout or archival of all measured product data.

f) Configurable levels of alarms and messaging for monitoring the loading and unloading operation.

g) Interface with meter proving operations.

h) In the event of a power loss during loading operations, the preset should be capable to retain and archive all measured data stored and in process if loading is in operation for retrieval when power is restored

15 Terminal Automation System

15.1 General When utilized, the Terminal Automation System (TAS) manages product distribution at the facility. Product is unloaded separately for each supplier, and product throughput is automatically reconciled over a configurable period, normally set to every 24 hours. Reports are automatically generated for each supplier and access to


information is fully password-protected. Automatic tank gauge systems can be connected to the TAS to provide a comparison between physical tank inventories versus calculated inventory based on throughput. Any differences are reported as gain/loss amounts for that period. The TAS should include the ability to account for bulk movements of product within the facility and product receipts or transfers to and from the facility.

The TAS can support both order-driven operations with preset amounts automatically downloaded to the electronic preset, and allocation-based operations where drivers enter a customer number and the desired preset amount of product on the electronic preset. This amount is checked against the customer’s product allocation before the load is authorized. The TAS should be capable of supporting unmanned operations at all times. Messages displayed at the loading and unloading should be simple and easy to understand to help reduce loading times.

(Relocated – Need to Review) The TAS should include the ability to provide net volume calculations. Refer to API MPMS Ch. 12.

15.2 Card Systems The terminal automation system may include the option to provide controlled access to and from the terminal using a card reader device installed at convenient locations where controlled access or activity is logged within the terminal. The card reader device may include a display to view message prompts and a keypad to enter data based on the messages displayed. The card reader devices are connected to the TAS to provide real-time communications for data entry validation. The operator or driver is responsible for placing the card in the card reader for a successful read to validate the card data, and for entering any unique PIN or additional information required. Cards can be used as a single device with additional prompts for supplier, customer, and vehicle information, or multiple cards can be used to provide this information. Data provided from the cards is used for security and also can be printed on the bill of lading.

15.3 Security The TAS can include multiple levels of password protection with log of user access by date and time and user ID. Any changes to the TAS configuration should be clearly traceable using an event log file and print out. An audit trial file and print out is also included to show all transactions of product movement at the terminal.

15.3 Bill of Lading Printers Bill of lading printers are connected to the TAS and print the bill of lading upon completion of load. Multiple bill of lading printers may be required to support printout of bill of lading at preferred locations or per supplier. No vehicle can leave the terminal without a bill of lading. The option should be available to withhold the bill of lading if loading information is not correct; this is especially important for additive amounts included with the main product. Requirements for information on the bill of lading vary by state and company. Data can include Department of Transportation information relating to the particular products.

16 LPG LPG loading and unloading metering systems require the same selection, installation and meter proving requirements of loading and unloading metering systems for other petroleum products.

Notable exceptions would be the use of air eliminators and excess flow valves. Air eliminators are not used in LPG systems. The system pressure is maintained to ensure the product remains in a liquid phase. Excess flow valves are safety devices used to stop flow in the event of a broken hose connection.

If truck and rail car loading or offloading for high vapor pressure products (i.e. LPGs) are equipped with vapor equalization lines connected to the supply or receiving vessel(s) the volume should be measured

16.1 Back Pressure The back pressure shall be adequate to keep the fluid in the liquid phase. For measurement purposes the pressure at measurement temperature should be twice the pressure drop across the meter at maximum operating flow rate,


or at a pressure 125 psi higher than the vapor pressure at a maximum operating temperature, whichever is lower. (See API MPMS Ch. 5.3 and Ch. 6.6.)

16.2 Odorization A system should be provided to inject the proper amount of odorant, if required. A means of verifying that the stenching equipment is functioning properly should be provided. Two independent means of verifying odorization are recommended.

Except where specifically excluded for special uses, odorant can be added to LPG to serve as a warning agent in the event of a leak. Odorant shall be accounted for on the final ticket.


Annex A: General considerations (Informative)

A.1 Design Considerations The design of systems for truck and rail, loading and unloading should consider the following:

A.1.1 Loading, unloading, Transloading Layout Consideration should be given to the physical configuration of the lanes or stations. The number of lanes, truck and rail car configurations, blending methodology, product availability, and piping configurations should be referenced.

The number of lanes or stations will depend upon expected facility throughput and planned facility operation. Provisions for future expansion should be considered.

Consideration should be given to the number of arms per product for facility utilization and product availability at each station. In some facilities, blending may only be required during certain times of the year or splash blending may be acceptable so there may be no need for every arm to blend. The number of arms per product is also affected by pumping capacity.

The design and layout of product headers and manifolds is critical. Piping should be designed to minimize pressure loss. Typical pumps are low head (low pressure) and any additional pressure loss will reduce resultant flow rates. Piping downstream of the physical blend location should be minimized to reduce or eliminate potential product degradation and contamination.

For commissioning and decommissioning related to start-up, maintenance, and repair work, the lines should have high point vents and low point drains to allow air to be bled or product to be safely drained. Note that air in the piping may create dangerous hydraulic shock within the piping system when pumps are operated.

A.1.2 Pumping Capacity and Flow Rates Achievable flow rates at a facility are dependent upon the considerations in Section 5.10 as well as pumping system capacity.

A typical product load profile consists of a low flow start-up to minimize splashing, vaporization and static electricity build-up, a high flow component, and then a low flow component just prior to shutdown to minimize system shock and the chances of overfill.

For hydraulically actuated valves, the valve that controls the load profile depends on sufficient and stable product pressure and flow to operate properly. If product pressure falls too low due to insufficient pump capacity, the flow control valve may not close as quickly as desired.

For all valves, if product flow is not sufficient, the flow control valve may open more than desired and lose its ability to properly control the flow rate.

The anticipated loading rates and pressures with single as well as multiple loading arm operation should be verified at both maximum as well as minimum flow rates.

Insufficient pumping capacity can also affect meter accuracy by causing changes in flow rate and pressure. Sufficient pressure in the system is required to provide adequate back pressure on the meter to prevent cavitation and inaccurate measurement or possible meter damage

Consideration should be given to the quality of the blend. It is important to maintain blend quality to meet clean air regulations and product standards. Off-spec blends can be costly and unusable. If desired flow rates cannot be met to maintain necessary recipe ratios, the blend accuracy can be affected. If rates become too low, the control valves


will have difficulty maintaining accurate control. Flow rates that are too low may also be out of the accuracy range of the meter. Both instances may cause inaccurate measurement and blends. Certain types of blending demand very tightly maintained flow rates and pressures to ensure proper blend percentages. In these scenarios meter and control valve sizing and selection is critical. Ratio blending is dependent upon proper hydraulic conditions. Wildstream and side stream ratio blending (see Figure B.2.2) requires that the slipstream product pressure be at least 25% higher than the mainstream product in order to ensure accurate blending.

To help maintain proper flow and pressure characteristics, it is common to size and stage pumps based on the number of arms being loaded at a given time. For example, with three pumps in parallel on a product header, one pump may run to satisfy two arms, the second pump would start to meet demand for a third and fourth arm, and the third pump would start for demands five and above. When multiple pumps are used in parallel to feed header piping as described above, all of the pumps should be the same size so they will contribute equally to the hydraulics. Another control possibility may include using a variable frequency drive (VFD) controlled pump to adjust to the desired rates and pressures.

A.2 Pressure Pressure drop calculations should be made for typical loading and unloading conditions. When adding valves to existing installations, the increased pressure drop across the system should be taken into consideration.

Pressure variations are important due to the effects of pressure on the liquid being measured. For example, a 10-12 psig change in pressure for regular gasoline typically results in a 0.01 percentage correction to the volume. For LPG, this same change in psig results in a 0.05 percentage correction to the volume.

Typically, loading and unloading systems run off high volume, low head (low pressure) pumps. If the pressure drop across the metering system becomes too great, it may cause the flow control valve to malfunction. This high pressure drop situation can create cavitation, poor flow control, inaccurate shutdown, and unsafe loading conditions.

A.3 Vapor Control Regardless of the type of loading that is used—either bottom loading or top loading—some vapor will be produced in the truck or railcar compartment. The turbulence of the incoming product and the rising liquid level will cause air and vapor to be dispersed either out the top of the truck or railcar compartment to the atmosphere or to a vapor-processing system. If the system is equipped with a vapor control system, EPA regulations address check valve installation.

To prevent vapors from escaping while loading product, attach vapor hoses to the tank truck. A vapor flow sensor, or vapor hose connection device may be located in the vapor return line or vapor hose at loading lanes to shut down the loading operation if no vapor is flowing or the hose is not connected to prevent pressurizing tank trucks and to ensure the vapor is not leaking into the atmosphere.

When a vapor recovery system is installed on a vehicle equipped with bottom loading, suitable hoses and terminations should be provided and connected to a dedicated vapor header (where existing). (See API RP1004).

See section 16 for details about LPG.

A.4 Thermal Relief Systems Thermal relief systems are required to prevent over-pressurization of the metering system. Any section of the piping that can be isolated by the closing of control valves, block valves, check valves, etc. shall be protected from over-pressurization. The integrity of the protection should be verified periodically because of its potential to impact measurement. Thermal relief lines should be located to minimize the potential for product bypass around the meter, which can affect measurement accuracy. Installation upstream of the main product meter is acceptable provided the product flow control valve will relieve internally when downstream piping experiences excessive pressure. If the flow control valve does not have integral pressure relief, thermal relief is recommended between the valve and the


load arm. For multi-product blending systems, consideration of where the thermal relief valve is discharged to should be taken into account so as not to mix or downgrade the product that receives it

A.5 Overfill prevention Emergency shutdown of a bottom loading system to prevent a compartment overfill initiated by a high-level shutdown device is addressed by API RP 1004.

A.6 Control Valves The flow control valve is typically controlled by an electronic preset to reduce the discharge rate at start-up or before shutdown, to control the delivery rate and to shut off the flow at the conclusion of the delivery. For flow control valves which rely on differential pressure for operation, care should be taken to ensure that operating pressures are stable and provide for adequate speed of operation.

Control valves are not typically considered a means of providing positive isolation when closed

Flow control valves should provide a smooth opening and closing and be capable of stable flow control, and accurate product flow shut-down.

Digital control valves utilize two solenoids that are actuated independently to control working pressures within the valves. Digital control valves may require adjustment to keep them operating as desired. If a digital control valve is not properly adjusted, it may open too quickly and or close too quickly. This could cause the valve to overshoot.

Pressure variation from any source (miss-adjustment of speed controls, staged, multiple meter runs, etc.) can influence the accuracy of the valve shutdown leading to undershoot, or overshoot, of intended delivery volume.

Valve control is a component of automated valve control, volume preset and delivery systems (see section 13).

Control valves that use motor operators should be evaluated if loads are stopped on a set-point because reaction times could be slow.

A.6 Top loading arms drop tube design Loading arms should be designed to reach all domes on a truck or railcar to avoid moving the truck or railcar. They should be equipped with an extended drop tube and either a deflector end or a 45º cut C tube end that will reach to the bottom of the truck or railcar and provide submerged filling.

A.7 Top loading arms and clearance Top loading arms should be designed to swing up to avoid interfering with trucks or railcars entering the loading area and should be counterbalanced by a spring or weight to enable easy positioning. If overhead clearance is insufficient for swinging the loading arm, the loading arm will need to be moved horizontally and the drop tube may need to be attached and detached at each loading dome on the truck or railcar.

A.8 Air eliminators Types of air eliminators may be vertical vessels, horizontal vessels, combination strainer/air eliminators and combination filter/air eliminators.

Horizontal or vertical air eliminators operate by significantly reducing the fluid velocity by expanding the cross sectional area of the pipe. This allows entrained gases and air slugs to escape upwards towards the top of the vessel where the air will escape.

Vertical air eliminators can also operate by using tangential nozzles that promote natural centrifugal forces that allow the liquid to move towards the vessel wall and downward while the air or gas moves towards the center of the vessel and upwards towards the top of the vessel where the air will escape.


Combination strainer with air eliminators operate by reducing the fluid velocity by expanding the cross sectional area of the pipe. This allows entrained gases and air slugs to escape upwards towards the top of the vessel where the air will escape.

Removal of air becomes more difficult as viscosity increases. With higher viscosity liquids, a larger capacity vessel may be required.

A.9 Overfill protection systems For bottom loading tank trucks and rail cars, an automatic tank overfill protection system is interlocked with the electrical system so that the product cannot be loaded without the overfill system being engaged. This precaution will minimize the chance of tank truck compartment overfill by closing the flow control valve when product is sensed at a specified level in the tank truck compartment. It is important that tank truck sensor heights are selected to provide enough compartment room to allow the control valve time to close without product spillage. Refer to API RP 1004, “Bottom Loading and Vapor Recovery of MC-306 & DOT-406 Tank Motor Vehicles” for guidance. For bottom loading light and heavy oil into rail cars, an automatic overfill protection system may be used or could be required by a regulatory agency. Other systems may rely on other types of overfill protection systems including visual processes to determine product level loaded.

For top loading tank trucks, and rail cars, an automatic overfill protection system should be considered. Top loading typically requires an operator/driver to be on the tank-loading platform and have manual control of a spring-loaded “dead man” valve during the filling cycle.

An offering facility shall have an overfill prevention system or procedure in place as a secondary safety system. It should not be used as the primary LTQ control. An overfill prevention system can be either automatic or manual. An automatic system is alarmed, typically visual and audible, for rail tank car loading operations and is activated without operator intervention. When an automatic protective action or alarm condition is received, the loading facility should confirm that the LTQ has not been exceeded. A manual alarm system requires operator action when an alarm is received, in accordance with terminal operating procedures. The alarm set points should be set to allow sufficient time for operations personnel to react and prevent any potential overfill or release. In determining protection levels to allow human reaction times, the pump rates from truck and tanks and maximum human reaction timeframes should be used. If an alarm overfill prevention system is not available, an operator should be physically present with an unobstructed view or with a measurement capability to ensure that a rail tank car is not overfilled. In the event that a rail tank car is overfilled, appropriate personnel should be notified in accordance with terminal operating procedures and steps should be taken to remove excess product from the rail tank car.


Annex B: Blending (Informative)

B.1 Blending This section discusses the design, selection, installation, operation, and performance, of product blending systems at truck and rail loading and unloading facilities.

The typical blending systems used are sequential blending, ratio blending, and side stream along with other combinations of these blending systems.

B.2 Sequential Blending

B.2.1 Splash Blending Splash blending is accomplished by manually loading individual components in the proper proportion according to the finished product recipe. Components are normally added one at a time through discrete product meters and loading arms (see Figure B.1.1).

Figure B.1.1—Typical Splash Sequential Blending


B.2.2 Automatic Sequential Sequential blending is accomplished by loading individual components in the proper proportion according to the finished product recipe. This is accomplished by opening product line block valves one at a time through one meter/load arm position in a set sequence to complete the finished product (see Figure B.1.2). For this arrangement, the meter needs to be proved on each product and the tickets need to be calculated using the unique meter factor associated with each product.

Figure B.1.2 —Typical Automated Sequential Blending

B.3 Ratio Blending

B.3.1 On Rack Ratio Blending On rack ratio blending is accomplished by simultaneously combining two or more products through dedicated unique meters in respective amounts and flow rates according to the finished product recipe. This is accomplished at the individual loading position while delivering into a truck or railcar. This process is typically automated (see Figure B.2.1). For this arrangement, all meters require proving.


Figure B.2.1—Typical On Rack Ratio Blending

B.3.2 Side Stream Blending On rack side stream blending is accomplished by simultaneously combining a minor product flow through a dedicated flow meter and control valve upstream of the major products meter and control valve. The minor product flow is controlled based on the blended stream. This process is typically automated (see Figure B.2.2). For this arrangement, the minor product flow meter does not require proving, but it may be necessary to assure proper blend ratio accuracy


Figure B.2.2—Typical Side Stream Blending

B.4 Hybrid Blending Hybrid blending involves blending components using both sequential and ratio or side stream techniques in combination on the rack.

B.4.1 Hybrid Ratio The blending is accomplished by simultaneously combining a ratio product with a sequential product stream through unique meters and control valves in respective amounts and flow rates according to the finished product recipe. This is accomplished at the individual loading position while delivering into a truck or railcar. This process is typically automated (see figure B.3.1).

Hybrid blending arrangements require proving for any meters that directly feed the final ticketed quantity.


Figure B.3.1—Typical Hybrid Ratio Blending

B.4.2 Hybrid Side Stream The blending is accomplished by simultaneously combining a ratio/minor product through a dedicated meter and control valve with a sequentially blended product upstream of the final blend meter and control valve. The two respective streams are proportionally blended according to the finished product recipe. This is accomplished at the individual loading position while delivering into a truck or railcar. This process is typically automated (see figure B.3.2).


Figure B.3.2—Typical Hybrid Side Stream Blending

B.5 Proportional and non-proportional blending

Ratio blending methods can be further classified as either proportional or non-proportional.

B.5.1 Proportional Blending

In this blending method, the flow of each component is controlled by the preset to ensure the final desired blend ratio is maintained throughout the entire loading process. The advantage is that the product being loaded is on specification throughout the entire course of the load. However, due to meter flow range limitations, this method may limit recipe options to percentages that are capable of being delivered within the flow ranges of the meters installed.

B.5.2 Non-Proportional Blending

In this blending method, the flow of each component is controlled by the preset, similar to the proportional method; however, some components may be loaded at a fixed flow rate or sequentially rather than being loaded proportionally throughout the course of the load. Nearly any ratio can be obtained with this approach. The disadvantage is that the product being loaded may not meet final specification until the completion of the load.


Annex C: Off Specification Product (Informative)

C.1 General A load arm or header used for any type of blending will retain product between the preset control valve and the load arm coupler or between the header and meter or both. If this system handles multiple products, the last product delivered in the recipe left in this section of piping may be sufficient to cause the next compartment to be off specification. This length of piping should be as small as possible minimize this retained product which may cause octane giveaway resulting in financial impacts or may result in blended products that are off specification such as biofuels, or dyed products. It may be necessary to provide an isolation means in each line as close to where multiple products meet as feasible to prevent back flow and line contamination.

Special care needs to be taken when dealing with pressure relief lines on blended product arms. If it is possible all product relief should return to its own product grade. For relief of sections of common pipe that may contain different products the piping should relieve to the least sensitive product.

The information management system should contain the information necessary to quantify the amount of each component which was blended and shipped.


Annex D: Additives (Informative)

D.1 General Additives are added to the main products dispensed at the loading rack as required during loading operations to enhance engine performance and meet regulatory requirements. These additives may be proprietary or common among multiple suppliers. Any additives dispensed shall be accounted for based on the required additive to main product ratio over a specified amount of product. Additives include dyes for tax-exempt use of product, detergents to assist in cleaner fuel burning, lubricity, and static dissipating, and odorants for LPG applications. Additive injection may be typically accomplished using electronically controlled meter-based injectors or mechanical piston-based injectors. The system should be capable of being monitored to provide alarms and shutdown during upset conditions.

Positive displacement pumps are typically used for additive systems. A pressure relief valve is required to be connected to the pump discharge to prevent over pressuring of the line because injectors operate on an intermittent basis and only when there is product flow. Because there will be times when there is no additive flow to the loading rack, an additive return line should be installed from the pump discharge to the additive tank to allow for flow back to the tank for times of reduced or no-flow conditions thus preventing over pressure of the line which could result in equipment damage, or environmental release.

The relief valve is normally set to a higher pressure to adequately inject the additive into the product stream to overcome the product loading pressure, pump dead head pressure at minimum flow with the product tank at the highest level.

Red dye is notorious for migrating and a very small amount can affect a large amount of product. For this reason it is strongly suggested that some type of additional shut off or flush mechanism be utilized as close to the actual injection point as well as a flush volume to keep from contaminating later loads. If a flush mechanism is utilized it should be sized and positioned to be able to flush all dye out of the line before the end of the load. If an additional shut off valve is utilized it should be installed as close to the pipe connection and with as small a diameter pipe as possible to minimize dye sitting in the line. Care should be taken in the design of the shut off system for dye as the additional shutoff valves or flush mechanism can create blocked in section of pipe which may need thermal relief.

D.2 Additive Meters Additives are generally measured and accounted for in cubic centimeters (cc). Additives are typically injected into the product stream in a parts per million ratio. Due to the low injection ratio and higher relative costs for additive the metering for additive becomes more important. Additives are typically injected in shots throughout the load to keep the ratio within specifications.

Additive is typically metered using a small volume oval or spur gear type positive displacement meter. The meter is typically outfitted with a pulser for electronic control and monitoring. High-resolution meters should be used for measurement of additive with an electronic pulse resolution of over 2,000 pulses per gallon. Higher resolutions of over 5,000 pulses per gallon are recommended for smaller amounts such as with dye injection. Additive tubing can be 1 in. or less to support additive injection with typical main product flow rates and typical additive treat rates between 0.05 – 1 gallons per thousand.

D.3 Calibration of Additive Injection The additive meter or cylinder should be calibrated using a calibration port on the additive injector panel to cycle a suitable amount of additive into a known calibrated container for comparison with the reported amount from the load rack electronics. A spring-loaded back pressure valve or equivalent should be used on the calibration port to simulate downstream line pressure as much as possible when proving metered additive panels.


A meter K-factor should be determined when using an electronic system to correct for inaccuracies. Mechanical cylinder volume adjustments are applied when using piston-based injectors. The calibration test should be repeated until the reported amount dispensed and the measured amounts are within the desired tolerance (typically 2%).

Additive should be calibrated with injection volumes that approximate the actual injection volume used for that meter.

Any device used for calibration shall have the resolution needed to meet the calibration resolution requirements for the injector.

D.4 Multiple Additives

For multiple additive applications where more than one additive is required at the load arm, the additives may be injected using a dedicated injector panel per additive or multiple additive injector panel. The loading rack electronics can be configured to deliver the exact amount of additive before a configured volume reaches the preset amount. This volume is normally the volume of liquid needed to flush the load arm from the point of additive injection to coupling with the vehicle. Once the additive is dispensed, an additive flush pump can be activated to provide the additional line pressure necessary to flush main product through the additive panel assembly. For instances where additives may be selected by product recipe, it is advisable to complete the additive injection by a predetermined volume prior to the end of load to allow the dispensed additive to flush into the vehicle and offer clear product for the next batch.


Bibliography

[1] API Manual of Petroleum Measurement Standards (MPMS), Chapter 4.2, “Displacement Provers” [2] API Manual of Petroleum Measurement Standards (MPMS), Chapter 4.4, “Tank Provers” [3] API Manual of Petroleum Measurement Standards (MPMS), Chapter 5.3, “Measurement of Liquid

Hydrocarbons by Turbine Meters” [4] API Manual of Petroleum Measurement Standards (MPMS), Chapter 7, “Temperature Determination” [5] API Manual of Petroleum Measurement Standards (MPMS), Chapter 9, “Density Determination” [6] API Manual of Petroleum Measurement Standards (MPMS), Chapter 11.2.1, “Compressibility Factors for

Hydrocarbons: 0 – 90 API Gravity Range” [7] API Manual of Petroleum Measurement Standards (MPMS), Chapter 11.2.2, “Compressibility Factors for

Hydrocarbons: 0.350 – 0.637 Relative Density” [8] API Manual of Petroleum Measurement Standards (MPMS), Chapter 11.3.3, “Ethanol Density and Volume

Correction Factors” [9] API Manual of Petroleum Measurement Standards (MPMS), Chapter 12.2, “Calculation of Liquid Petroleum

Quantities by Turbine or Displacement Meters” [10] API RP 1004, Bottom Loading and Vapor Recovery for MC-306 Tank Motor Vehicles [11] API RP 2610, Design, Construction, Operation, Maintenance and Inspection of Terminal and Tank Facilities [12] NIST Handbook 12, Examination Procedure Outlines for Weighing and Measuring Devices [13] NIST Handbook 105-3, Specifications and Tolerances for Reference Standards and Field Standards

Weights and Measure, Specifications and Tolerances for Graduated Neck Type Volumetric Field Standards

Documents

Manual of Petroleum Measurement Standards Chapter …ballots.api.org/copm/colm/ballots/docs/COLM_6 _2A_1_18.pdfChapter 6—Liquid Flow Measurement Systems Section 2A— Truck and Rail